GENEVA, March 12 (Reuters) - Syrian opposition negotiator Mohamad Alloush said on Saturday that Syria's political transition could only start once Bashar al-Assad was no longer president of Syria.

"We consider that the transitional period starts with the fall of Bashar al-Assad or his death," he told reporters in Geneva, where a round of peace talks is due to begin on Monday.

"There's no possibility to start this period with the presence of this regime or the head of this regime in the power."

He described as "worthless" a statement by Syrian Foreign Minister Walid al-Moualem earlier on Saturday that the presidency was not up for discussion at the talks. (Reporting by Marina Depetris, Firas Makdesi and Yara Abi Nader; writing by Tom Miles; Editing by Kevin Liffey)